Liquid crystal display is mainly composed of an opposite substrate, an array substrate, and a liquid crystal layer located between the two substrates. Generally, patterns such as gate lines, data lines, thin film transistors (TFT) and pixel electrodes are arranged on one side of the array substrate. A TFT specifically comprises: a gate electrode and an active layer mutually insulated; a source electrode and a drain electrode electrically connected to the active layer respectively; wherein the gate electrode is electrically connected to the gate line, the source electrode is electrically connected to the data line, the drain electrode is electrically connected to the pixel electrode. Patterns such as black matrix and color films are arranged on one side of a color film substrate.
At present, in the existing manufacturing process of the array substrate, usually a one-time composition process is adopted to form the patterns of a gate electrode 102 and a gate line 103 on an underlay substrate 101, as shown in FIG. 1a; then a gate insulating layer is formed on the underlay substrate 101; a pattern of an active layer 104 is formed on a region of the gate insulating layer corresponding to the pattern of the gate electrode 102, as shown in FIG. 1b; then a pattern of a etching barrier layer 105 is formed, as shown in FIG. 1c; a one-time composition process is adopted to form the patterns of a source electrode 106, a drain electrode 107 and a data line 108, as shown in FIG. 1d; finally, a pattern of a pixel electrode 109 electrically connected with the drain electrode 107 is formed, as shown in FIG. 1e. After the pattern of the pixel electrode 109 is formed, patterns of an insulating layer and common electrodes 110 are typically formed, as shown in FIG. 1f. 
After the patterns of the source electrode, drain electrode and data line are formed, a pattern of the pixel electrode is typically formed with a photolithography process, i.e., an indium tin oxides (ITO) film and a photoresist film are formed in sequence by stacking on the patterns of the source electrode, drain electrode and data line; then the photoresist film is treated with exposure and development processes; an etching process is performed with etching agent for the ITO film on which the photoresist does not cover, wherein the region treated by the etching process comprises the ITO film covering over the source electrode and the data line; finally, the remaining photoresist is peeled off to obtain the pattern of the pixel electrode.
In the specific implementation, metals such as copper are commonly used for the patterns of the source electrode, the drain electrode and the data line; in such a manner, during the etching process for the ITO film covering over the patterns of the source electrode and the data line, etching agent will be in direct contact with the source electrode and the data line, resulting in corrosion of the source electrode and the data line; moreover, the high temperature environment during the subsequent forming of insulating layer will accelerate the corrosion process, which will affect the display quality of the liquid crystal display.
Therefore, how to avoid the source electrode and the data line being corroded by the etching agent is a technical problem to be solved by those skilled in the art.